The Nutrients
People eat to receive nourishment. To maintain your “self,” you must continually replenish, from foods, the energy and the nutrients you deplete as your body maintains itself.
There are six classes of nutrients: Carbohydrates, Lipids (fats), Proteins, Vitamins, Minerals, and Water.
First of all, we will talk about the energy-yielding nutrients which include carbohydrates, fats, and proteins. They are sometimes called macronutrients because they are needed by the body in relatively large amounts (many grams daily). In contrast, vitamins and minerals are micronutrients, required only in small amounts (milligrams or micrograms daily). The energy released from carbohydrate, fat, and protein can be measured in calories. Energy is expressed in 1000-calorie metric units known as kilocalories.
The amount of energy a food provides depends on how much carbohydrate, fat, and protein it contains. When completely broken down in the body, a gram of carbohydrate yields about 4 kcals of energy; a gram of protein yields about 4 kcals; and a gram of fat yields 9 kcals. Because fat provides more energy per gram, it has a greater energy density than protein or carbohydrates.
The processes by which nutrients are broken down to yield energy or used to make body structures are known as metabolism.
Next, we will talk about the vitamins. They are organic but do not provide energy. Instead, they facilitate the release of energy from carbohydrate, fat, and protein and participate in many other activities throughout the body.
Vitamins can function only if intact, but they are vulnerable to destruction by heat, light, and chemical agents. The strategies of cooking veggies at moderate temperatures for short times and using small amounts of water help to preserve the vitamins.
There are only 16 minerals known to be essential in human nutrition. Because minerals are inorganic, they are indestructible and need not be handled with the special care that vitamins require.
Lastly, water provides the environment in which nearly all the body’s activities are conducted. It participates in many metabolic reactions and supplies the medium for transporting vital materials to cells and carrying waste products away from them.
In summary, foods rich in energy-yielding nutrients provide the major materials for building the body’s tissues and yield energy for the body’s use or storage. Energy is measured in kcals. Vitamins, minerals, and water facilitate a variety of activities in the body.